More X-Chromosome Charts
Last month I wrote “Unlocking the Genealogical Secrets of the X Chromosome” and posted a few charts that show the inheritance of the X-chromosome through 8 generations. I thought these charts might be helpful since inheritance of the X-chromosome can be difficult to understand without seeing it.
New Chart with Ahnentafel Numbers
Since posting the article, two new charts have been created using the originals. I made one, and the other was made by Rodney Jewett (who gave me permission to re-post the chart here) and posted at dna-forums.org.
Mr. Jewett added the Ahnentafel numbers of contributing X-chromosome ancestors to the chart. Using these numbers, an individual can simply create a numbered Ahnentafel report to identify X-chromosome contributing ancestors using this chart:
Note that Ann Turner also has a text file of the Ahnentafel numbers of those ancestors who potentially contributed to the X chromosome, through 10 generations.
New Chart Showing Contribution Percentages
I’ve been very intrigued by all the recent discussion of the X-chromosome in the genetic genealogy context, and I’ve been exposed to some facts about the X-chromosome of which I previously was unaware.
For instance, I kept seeing statements that suggested that different ancestors in each generation contributed different amounts to the X chromosome. I read that at the 8th generation, one ancestor contributes 1/8th, some contribute 1/64th, and the others contribute between 1/16th and 1/32nd. I kept trying to understand this, but I had to chart it out to grasp it. Although this chart is for a male, I believe it will also work for a female by adjusting the generations slightly. The chart is big so it might take a moment to download:
Thus, the chart shows that if you are a male, your mother’s father’s mother’s father’s mother’s father’s mother contributed 1/8th of your X-chromosome, while your mother’s mother’s mother’s mother’s mother’s mother’s parents only contributed 1/64th.
Now, keep in mind that this chart serves only as a very rough guideline for inheritance. Although males pass the X chromosome largely unchanged to their daughters, females will usually pass a mixed X chromosome to their child a mixture of the X chromosome they received from their father and the X chromosome they received from their mother. However, a child is unlikely to receive an X chromosome from their mother that is 50% from their maternal grandfather and 50% from their maternal grandmother – it will most likely be some other more random amount between 0% and 100%. Thus, an ancestor is likely to be either under- or over-represented in an actual X chromosome.
Please, if you find any errors in my chart, please feel free to email me and I’ll do my best to correct them.
Potential Research
With the advent of affordable sequencing, I would love to see a study that examined X-chromosome inheritance in a family of 6 or 8 generations. How closely would it match the theoretical inheritance probabilities from the chart above? It’s probably just a matter of time before this research is conducted.
P.S. – Feel free to use these charts, but please give proper credit.


Last week, Randy Seaver of Genea-Musings 
Terry Barton is co-founder of
If you’ve ever even thought about testing your own DNA for genealogical purposes, then you are almost guaranteed to have heard of
Genetic genealogy has been commercially available since 2000, and in the last 8 years many genealogists have used this new tool to learn about their ancestry. Over the course of the next two weeks, I will be sharing interviews I recently conducted with 9 individuals who have had a huge impact on the field of genetic genealogy. The list includes – in the random order that their interview will appear – Bennett Greenspan, Megan Smolenyak Smolenyak, Terry Barton, Alastair Greenshields, Whit Athey, Ann Turner, Katherine Hope Borges, Max Blankfeld, and Ana Oquendo Pabón.
